It is well known that hills, valleys, trees and buildings affect the velocity of the wind, the wind's direction and turbulence. Most wind power systems are operated in open rural regions with little or no obstructions and few nearby neighbors. The systems include large nacelles with large hub assemblies. The hub assemblies which typically include two to three long solid blades are mounted on the end of a tower that holds them a sufficient elevation above the ground to reach ‘clean’ or low turbulence wind.
Large wind power systems found in the prior art typically use high RPM, low torque synchronous generators the produce electricity when the sustainable winds are within a narrow range of velocities. Because such generators require high input shaft velocities, gear boxes are placed between the hub assemblies and the generators. When the velocity of the wind is below the desired velocity range, the hub assemblies are disconnected from the generators. When the wind velocity is above the desired velocity range, the blades are rotated or furled to allow a greater percentage of the wind to flow in between the blades and thereby reduce rotation. In high velocity winds, a dynamic brake may be used to reduce or stop rotation.
High torque, low RPM, asynchronous generators, on the other hand produce electricity at lower RPMs. The amount of electricity produced by asynchronous generators is determined by the generator shaft's RPMs and the amount of torque applied to the shaft. The shaft's RPMs and the torque are determined in part by the number of blades on the hub assembly and the surface area of each blade.
The swept area is the area of a circle the blades of a wind generator create when rotating. The greater the swept area, the greater energy can be captured from the wind and more electrical energy can be produced.
The power produced by the blades on a wind generator system, is the product of shaft RPM speed and torque. To transfer power, a rotating shaft can operate either at high speeds and low torque, or at low speeds and high torque. As the number and lengths of the blades on a hub assembly increases, the hub's RPMs decrease and the torque increases. Conversely, as the length of the blades decrease, the hub's RPMs increase and the torque decreases.
The swept area of a horizontally aligned wind turbine is determined by the equation: π×r2. When the swept area is evenly divided into concentric rings, the swept area of the outer rings are greater than the swept areas of the inner rings.
Because the power of the wind (P) at a velocity (V) is determined by the equation P=(½)×(π)×(Air Density)×(V), turbines generators that use blades with a fixed length are best suited for locations with constant, moderate winds. Most locations are exposed to irregular, variable winds.
What is also needed is a wind generator system that uses lightweight blades that longitudinally adjust their lengths to increase or decreasing the swept area enabling it to operate more efficiency in low wind conditions and protect the wind generator in high wind conditions.
What is also needed is a wind generator system that uses lightweight blades that can also change their surface areas.